As the communication services have developed continuously, the demands on the transmission bandwidth of the communication network become increasingly high. One effective solution for improving the transmission bandwidth is to combine optical signals with a plurality of wavelengths into one signal (wavelength division multiplexing, WDM) for being transmitted via optical fibers. However, in a WDM system, especially a dense WDM (DWDM) system (for example, a WDM system with a wavelength interval smaller than or equal to 50 GHz), the wavelength interval between two neighboring channels is rather narrow, so the demands on the accuracy and stability of the wavelength of each optical signal to be multiplexed are quite high.
According to a conventional wavelength locking solution, during the operation process of the system, the wavelength or the accurate wavelength offset of each optical signal is detected by a wavelength detector, and according to a detection result, a feedback is given, so that the wavelength of the signal output from the laser is controlled. In this manner, the wavelength detector for each signal is required to have a high accuracy. Meanwhile, in order to lock the wavelength, the wavelength control at each channel requires using a set of control loops, the structure is rather complicated, and the volume power consumption is fairly large.
In a first solution of the conventional art, as shown in FIG. 1, an optical signal output from each laser is split into two channels of signals by an optical splitter, the signal in one channel is input to a combiner for being combined and then output, and the other signal is input to the wavelength detector for wavelength detection. Each laser requires one optical splitter and one wavelength detector, so that it requires a great number of elements, and has a complicated circuit structure, and a high cost. For the element with a high integration level, sometimes, the splitting and detecting operations of each optical signal even cannot be realized. Each optical signal in each channel is extracted before being combined. However, as for the element with a high integration level, for example, a photonic integrated circuit (PIC), signals from n channels of lasers are output after being combined in the element package, so that the signal in each channel before being combined cannot be extracted, so the wavelength thereof cannot be detected and controlled.
In a second solution of the conventional art, as shown in FIG. 2, the optical signal obtained after being combined firstly passes through one optical splitter, and then a part of the optical signal is directly output, and the optical splitter outputs the other part of the signal to each laser respectively, so as to detect the wavelength and control the wavelength thereof. Thus, each laser requires a wavelength detector, which thus requires a great number of elements, and has a complicated circuit structure, and a high cost. The wavelength detector of each laser is required to have a single channel filtering function.